Macroporous, perforated films are commonly used for vapor and liquid permeable applications, whereas microporous perforated films are useful for vapor permeable applications, but not liquid permeable applications. Macroporous perforated films are commonly used as components in personal care garments (e.g., diapers and feminine hygiene products). Perforated films are also used in filtering, and acoustic applications.
Macroporous permeable films are commonly made by first producing a continuous film and then subjecting the film to a perforation process. Mechanical perforating devices include intermeshing rollers, die punching, or needlepunching. Films can also be perforated using perforated rollers having thermal zones or lasers that melt perforations into the film. Other techniques for providing the perforations include casting a film on to a porous quench roll that has vacuum on the holes to pull the melt into the hole and produce an aperture, using electrical corona treatment to create perforations by localized energy treatment, and creating perforations is by blending immiscible materials followed by film stretching to create perforations by generation of film voids. It is also known that after quenching polypropylene in to beta phase crystals, upon orientation, the film will become porous.
There exists a need for additional techniques, preferably relatively simple and economical, to make composite layers (including films and sheets) that possess blind holes that penetrate through some, but not all, of the layers.